Standard techniques for creating 3D topographies include stylus instruments, profilometers, ultrasonic transducers, and laser triangulation among others. Shape-from-shading (SFS) and photometric stereo (PMS) have been used to create topographies by illuminating a specimen 1 with one or more a light sources 2, 3 directing oblique light 4, 5 toward the specimen 1 at an angle from 5 to 85 degrees and more typically from 25 to 75 degrees, as generally represented in FIG. 1. The oblique illumination is reflected from the surface S of the object as reflected light 6, and is captured by an image sensor (not shown) such as a CCD or CMOS sensor of a digital camera 7. The light sources are moved to different positions located circumferentially around the object, with images taken at these different positions. These images are used to calculate the topography of the specimen 1 by known means, employing appropriate processor(s) 8.
A standard reflected light microscope employing brightfield and darkfield functionality is shown in FIGS. 2 and 3. In this example the microscope 10 is equipped with a camera 12. Oculars may also be present, such that the numeral 12 is to broadly represent oculars and/or a camera. Although the following description will refer to a reflected light microscope, similar techniques apply to transmitted light microscopes or instruments using brightfield/darkfield microscope objectives. A reflected light microscope 10 will be referenced in the following descriptions but the technology may apply to any imaging system using a brightfield/darkfield objective. The systems generally consist of a light source 14 providing light 24, a vertical illuminator 16, a brightfield/darkfield (BD) switch 18 and a BD objective 20. U.S. Pat. Nos. 3,930,713 and 4,687,304 describe a BD objective. In a standard BD objective 20, two channels are provided to guide the light to the specimen 1. The light 24 is directed to a mirror 25 that reflects the light 24 toward the specimen 1 downwardly through the vertical illuminator 16, the nosepiece 28, and BD objective 20. The BD switch 18, as schematically shown, serves to limit the light 24 to pass either into a brightfield channel 22 or darkfield channel 26 separated by a shield wall 21. With the BD switch 18 in a bright field position as in FIG. 2, the light 24 is limited to a beam that is reflected off of the mirror 25 to enter the brightfield channel 22, which directs the illuminating light 24′ through the BD objective 20 toward the surface S of the specimen 1 at an angle perpendicular (90 degrees) to the plane of the specimen 1 and allows the reflected light 30 to pass to the oculars or camera 12. As seen in FIG. 3, when the BD switch 18 is in a darkfield position the light 24 is limited to an annular beam that is reflected off of the mirror 25 to enter the darkfield channel 26, which is an annular channel directing illuminating light 24″ toward the specimen at an angle less than 90 degrees and typically 25 to 75 degrees.
It can be seen in FIG. 2 that the light path in brightfield (illuminating light 24′) is projected through the center of the nosepiece 28 and through the brightfield channel 22 of the BD objective 20. The reflected light 30 is reflected back through the brightfield channel 22, through the nosepiece 28 and tube lens 32 and is affected by any oculars and/or captured by a camera 12. It is seen here that the illumination light 24′ in brightfield is at 90 degrees to the surface S of the specimen 1 and the reflected light 30 that is measured travels parallel to the illumination light 24′ but in an opposite direction. The projected illuminating light 24′ illuminates the entire field of view.
FIG. 3 shows the microscope 10 in darkfield mode. Here the light 24 is blocked by the darkfield switch 18 so that no light passes through the brightfield channel 22 and is instead directed to pass through the darkfield channel 26 as illuminating light 24″. This produces an annular beam (or, in other terms, a hollow cylinder or annular cylinder) of light that is projected toward the specimen 1 at an oblique angle determined by the design of the objective 20 and wall of the darkfield channel 26. As known, the BD objective will have mirrors and/or prisms and/or light diffusers built into the objective to direct the oblique light. The illuminating light 24″ reflects off the surface S of the specimen 1 and the reflected light 30 travels up the brightfield channel to the ocular or camera 12. The projected darkfield illuminating light 24″ illuminates the entire field of view from about the entire periphery (360 degrees) of the objective.
In brightfield imaging it can be seen that the field of view F, which takes in at least a portion of the specimen 1, is filled by direct 90 degrees illumination (the incoming illuminating light 24′ is orthogonal to the general resting plane of the specimen 1) whereas in darkfield imaging, the field of view F is filled by oblique illumination (the incoming illuminating light 24″ is at an oblique angle to the general resting plane of the specimen 1). The darkfield illumination is evenly distributed through the 360 degree circumference of the BD objective 20.